There are currently four licensed test kits used to detect antibody to hepatitis B surface antigen (anti-HBs). This study was designed to evaluate kit to kit and method to method analytical sensitivity (detection) variation. Analytical sensitivity in this context is defined as the lower limit of detection (i.e., the dilution at the cutoff). Interpolated dilution endpoints varied with HBsAg subtype and test kit. CBER Reference Panel #3 Anti-HBs(ad) endpoints ranged from a minimum of 1 76 to a maximum of 1 539 with all test kit methods giving a variation w7-fold. CBER Reference Panel #3 Anti-HBs(ay) endpoints ranged from a minimum of 1 242 to a maximum of 1 1223 with all test kit methods giving a variation W5-fold. This study demonstrates that a large variation of the minimum detection limit exists with currently licensed anti-HBs test kits. This variation can have a significant effect on the interpretation of test results depending on the intended use (diagnostic, prognostic, vaccine monitoring or anti-HBs content monitoring in Source Plasma).